Patent GB-698015-A (GB)
Title: Improvements in and relating to machine tapping
IPC: B23G1/16
Filed: 1951-09-12
Abstract: 698,015. Tapping; drilling. ALLEMANN AKT.-GES., H. Sept. 12, 1951 [Sept. 13, 1950], No. 21483/51. Class 83 (iii). [Also in Group XXIV] A screw-tapping machine has a sliding coupling 7 between the tap spindle 6 and driving spindle 5 and a compression spring 11 between an adjustable stop 12 and a pressure disc 13 bearing on the coupling so that, when the head 1 is lowered until the tap contacts the work, the upper arm 2 of the head compresses the spring by the amount d, Fig. 2, and the tap is applied to the work under spring pressure additional to the weight of the spindle 6 and chuck 9. The tap is then rotated and, as it cuts into the work, the advance of the spindle 6 relative to the head causes the lower end of the coupling to contact the disc 13 and allows the spring to expand to its uncompressed length so that its pressure drops to zero and the tap continues to feed without the aid of the spring. The tap is rotated for a certain number of revolutions to cut to a predetermined depth, reversed to rotate the same number of revolutions in the opposite direction and is then lifted from the work. The spindle 6 is axially displaceable in the arms 2, 3 of the head and has limited radial play in the lower arm 3 to allow alignment of the tap with the hole. Reversing mechanism.-The forward and reverse rotation of the driving spindle 5 is obtained by a rack 25 which engages teeth 24 on the hub of a pinion 23 journalled on a main shaft 21 and is connected to a crank-pin 26 adjustable in a crank-arm 27 driven from the main shaft through back gears 33 ... 31. The gear 31 is rotatable between a disc 29 fixed to the boss of the crank-arm 27 and a disc 30 rotating with the disc but capable of axial displacement against the action of a spring to engage the gear 31 and form a friction clutch. The disc 30 is movable by screws 35a in a plate 34 attached to the crank-boss, the screws being rotated synchronously by gears 35 engaged by a central gear 36. Drilling.-A gear 22 is fixed on the main driving-shaft 21 and sliding shafts 37 having gears 38 may be engaged either with the continuously-rotating gear 22 or the reversing gear 23 to drive a number of circularly-arranged spindles for either drilling or tapping, as required. Stop-motions.-The automatic operation of the machine is controlled by contact rollers and eccentrics and an electro-magnetically-operated safety-device is provided for stopping the machine if a fault arises, and for operating an alarm signal. The device comprises an adjustable insulated spring contact 17, Fig. 3, and a collar 15 below the pressure disc 13. At rest, the contact lies between the disc and the flange but when the head 1 is lowered the contact also moves down to engage the collar. Its circuit is not, however, completed by the control eccentrics until the tap has rotated sufficiently for the collar to have moved down, out of engagement with the contact. If, however, the tap is dull and does not enter the work, the disc and collar do not move down and the contact 17 and collar 15 remain engaged, maintaining the safety circuit closed. If the tap has broken during the preceding operation, the spindle 6 can move down to keep the safety circuit closed through the contact 17 and the disc 13. For preventing the tap from cutting beyond the predetermined depth, the safety circuit may include a contact on the spindle co-operating with an insulated contact on the machine frame.